The container may be, for example, a tube made of plastic or one made of its aluminum plastic laminate, which is usually sealed at its one end by means of a cover or a cap and by means of a weld seam running transversely or vertically to the longitudinal extension of the tube at its opposite end. However, the container may also be a bag consisting of plastic film or of the said laminate and in particular a so-called tube-like bag, which is sealed at its both opposite axial ends each via a weld seam running transversely to the longitudinal extension. By way of example, it shall be assumed below that the container is a tube; however, the present invention is not limited thereto.
Tubes are predominantly used for accommodating pasty products, for example, a cream, which the user presses out after opening a seal by means of applying an external force of pressure on the tube. When the weld seam sealing the tube at its rear end is leaky, the problem arises in this connection that the product likewise leaks out there in an undesired manner. In order to prevent this, it is known to monitor the process parameters precisely and to check the tubes for their tightness after the filling and sealing, since leaky tubes lead to high image damage and additional costs for the manufacturer on the market.
The tightness of a tube is usually tested randomly. For this, a sealed tube is removed from the tube-filling machine or filling process and an overpressure is applied by means of compressed air in the tube interior in a separate test station. For this purpose, the tube seal must be opened beforehand, as a result of which the tube is unsaleable and must be disposed of after the testing.
As an alternative, a force of pressure from outside is exerted on the tube wall and then it is detected whether the weld seam opens and the product leaks out. When the product leaks out, the test station must be cleaned. A corresponding cleaning is time-consuming and costly.
A fundamentally different process for the tightness check of a tube consists of introducing a test gas together with the product into the tube and locking it in same. It is subsequently detected by means of a test probe whether the test gas leaks out from the interior space of the tube. The costs of a corresponding device are very high as a result of the relatively expensive sensor mechanism and also as a result of the relatively large amount of test gas needed. In addition, the process works relatively slowly, such that the performance of a corresponding tube-filling machine is reduced. In case of sensitive and high-value products, it is frequently not desired to weld the test gas into the tube and thus to expose the product to the effect of the test gas. In addition, only the gas-tightness of the tube is checked in this way and it is not taken into consideration what stresses a user of the tube applies to same during use.